1. Field of the Invention
The present invention relates to an apparatus for cleaning a rotating drum of an electrophotographic copying machine. In general, a transfer type electrophotographic copying machine or apparatus includes a rotatable drum having an outer cylindrical surface provided with a photo-conductive layer in which an electrostatic latent image of an original to be copied is produced during the rotation of the drum and subsequently developed by a toner, the developed toner image being then transferred to a transfer sheet such as plain paper. In such copying machine, it is required to remove the toner particles possibly remaining as deposited on the outer surface of the drum even after the image transfer has been finished. The invention is directed to an apparatus for cleaning the drum in this sense.
2. Description of the Prior Art
In a hitherto known drum cleaning apparatus of the type described above which includes a rotatable drum 1 rotated about a horizontal axis in the direction indicated by an arrow in FIG. 1 of the accompanying drawings, a cleaning blade 2 which is referred to as the doctor blade is so disposed relative to the drum 1 that the lower edge is brought into contact with the outer cylindrical surface of the drum at a portion moving upwardly as shown in FIG. 1.
Through the sliding movement of the blade 2 on and along the outer cylindrical surface of the drum 1, the toner particles deposited on the drum surface are scraped off as the drum is rotated.
The toner particles T thus scraped off from the outer cylindrical surface of the drum will fall along an arcuate path corresponding to a segment of the outer cylindrical surface of the drum 1 delimited by the cleaning blade 2 and then fall freely downwardly. Accordingly, it is certainly possible to collect the toner particles by a container disposed in the free falling path of the toner particles.
However, this arrangement requires disadvantageously a relatively large occupation space around the cylindrical surface of the drum 1. With a view to avoiding such difficulty, it has been already known that the toner collecting container 3 is disposed at a relatively great distance from the drum 1, wherein the toner particles falling along the outer cylindrical surface of the drum are deflected toward the collecting container 3 by way of an inclined guide plate 4 having an upper edge bearing on the outer cylindrical surface of the drum 1 at the upstream side of the scraper blade 2 as viewed in the rotating direction of the drum 1, and lower edge positioned at the inlet opening of the container 3 thereby to introduce the toner particles therein from the outer surface of the drum.
With the toner collecting arrangement just described above, it is necessary that the upper edge of the guide plate 4 is in contact with the outer cylindrical surface of the drum under a constant and small pressing force uniformly over the whole width of the upper edge thereby to prevent accumulation of the toner particles on the guide plate 4.
In practice, however, the loose fluidity or mobility of the toner particles is often degraded in dependence on the environmental conditions prevailing in the copying machine (e.g. humidity is the most influential factor).
In such case, the toner particles scraped off from the drum surface will not be smoothly introduced into the collecting container 3 but deposited and progressively accumulated on the surface of the guide plate 4, as a result of which the toner particles T will overflow from the gude plate 4 on the way to the collecting container 3 and will cause undesirable contamination of the drum as well as of the interior of the copying machine.
Besides, there may occur such situation that the angle as well as pressing force at which the guide plate 4 bears on the outer surface of the drum 1 will undergo variation, whereby the toner particles T are scraped off from the drum by the guide plate 4 and hence the photo-sensitive layer may be eventually injured.
As an attempt to deal with the problem described above, it is conceivable that vibration or intermittent shocks are applied to the guide plate 4 thereby to promote a more smooth movement of the toner particles on the guide plate 4. However, application of such vibrations or intermittent shocks in an uncontrolled manner will exert adverse influence to the adjusted contact between the upper edge of the guide plate 4 and the outer surface of the drum 1, involving the separation of the former from the latter.
In other words, it is necessary that the shocks or vibration has to be so controlled that substantially no displacement of the guide plate 4 relative to the drum surface will occur, while the sliding down of the toner particles is promoted.